Process for the preparation of 8-(4-aminophenoxy)-4H-pyrido[2,3-B]pyrazin-3-one derivatives

ABSTRACT

The present invention pertains generally to the field of organic chemical synthesis, and in particular to certain methods for the synthesis of 8-(4-aminophenyoxy)-4H-pyrido[2,3-b]pyrazin-3-one and related compounds (denoted herein as (3)) from 4-(4-aminophenyoxy)pyridine-2,3-diamine and related compounds (denoted herein as (1)), by reaction with glyoxylic acid (denoted herein as (2)). The compounds (3) are useful in the synthesis of known anti-cancer agents, such as 1-(5-tert-butyl-2-(4-methyl-phenyl)-pyrazol-3-yl)-3-[2-fluoro-4-[(3-oxo-4H-pyrido[2,3-b]pyrazin-8-yl)oxy]phenyl]urea.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of PCT/GB2014/053489filed Nov. 25, 2014, which claims priority from UK Patent ApplicationNo. 1320732.9, filed on Nov. 25, 2013. Each of the prior mentionedapplications is hereby incorporated by reference herein in its entirety.

RELATED APPLICATION

This application is related to: United Kingdom patent application number1320732.9 filed 25 Nov. 2013, the contents of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention pertains generally to the field of organicchemical synthesis, and in particular to certain methods for thesynthesis of 8-(4-aminophenyoxy)-4H-pyrido[2,3-b]pyrazin-3-one andrelated compounds (denoted herein as (3)) from4-(4-aminophenyoxy)pyridine-2,3-diamine and related compounds (denotedherein as (1)), by reaction with glyoxylic acid (denoted herein as (2)).The compounds (3) are useful in the synthesis of known anti-canceragents, such as1-(5-tert-butyl-2-(4-methyl-phenyl)-pyrazol-3-yl)-3-[2-fluoro-4-[(3-oxo-4H-pyrido[2,3-b]pyrazin-8-yl)oxy]phenyl]urea.

BACKGROUND

A number of publications are cited herein in order to more fullydescribe and disclose the invention and the state of the art to whichthe invention pertains. Each of these references is incorporated hereinby reference in its entirety into the present disclosure, to the sameextent as if each individual reference was specifically and individuallyindicated to be incorporated by reference.

Throughout this specification, including the claims which follow, unlessthe context requires otherwise, the word “comprise,” and variations suchas “comprises” and “comprising,” will be understood to imply theinclusion of a stated integer or step or group of integers or steps butnot the exclusion of any other integer or step or group of integers orsteps.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context clearly dictates otherwise. Thus, for example,reference to “a pharmaceutical carrier” includes mixtures of two or moresuch carriers, and the like.

Ranges are often expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by the use of the antecedent “about,” itwill be understood that the particular value forms another embodiment.

This disclosure includes information that may be useful in understandingthe present invention. It is not an admission that any of theinformation provided herein is prior art or relevant to the presentlyclaimed invention, or that any publication specifically or implicitlyreferenced is prior art.

Springer et al., 2009, describes certain compounds including, forexample, compound AA-018 shown below, which are useful, for example, inthe treatment of cancer.

1-(5-tert-butyl-2-(4-methyl-phenyl)-pyrazol-3-yl)-3-[2-fluoro-4-[(3-oxo-4H-pyrido[2,3-b]pyrazin-8-yl)oxy]phenyl]urea (AA-018)

Springer et al., 2009 also describes methods of preparing suchcompounds. As part of those methods, the3-oxo-4H-pyrido[2,3-b]pyrazin-8-yl group is formed in a mixture of tworegioisomers (the 2-oxo and 3-oxo regioisomers) by a cyclisationreaction of a 2,3-diamino-4-oxy-pyridyl compound with ethyl glyoxylate,as illustrated in the following scheme (drawn from Synthesis 27therein).

The method used in Synthesis 27 therein is described as: “Using MethodD1 with tert-butyl 4-(2,3-diaminopyridin-4-yloxy)-2-fluorophenylcarbamate (3.50 g, 10.5 mmol), tert-butyl2-fluoro-4-(2-oxo-1,2-dihydropyrido[2,3-b]pyrazin-8-yloxy) phenylcarbamate (2.71 g, 69%) and tert-butyl2-fluoro-4-(3-oxo-1,2-dihydropyrido[2,3-b]pyrazin-8-yloxy) phenylcarbamate (0.96 g, 25%) were obtained.”

For reference, “Method D1” is described in the context of Synthesis 25therein as: “tert-butyl 4-(2,3-diaminopyridin-4-yloxy)phenylcarbamate(0.86 g, 2.71 mmol) was dissolved in 15 ml of dry ethanol; 0.8 ml (4mmol) of a 50% ethyl glyoxylate solution in toluene were added and thesolution was stirred overnight at room temperature under Argonatmosphere. The solvent was partially evaporated, and tert-butyl4-(2-oxo-1,2-dihydropyrido[2,3-b]pyrazin-8-yloxy)phenylcarbamate (0.430g, 45% yield) is precipitated by addition of acetone (10 ml) andfiltered off.”

Such cyclisation methods suffer from low yield. In addition, bothregioisomers are formed, and the undesired regioisomer (“2-oxo”) isformed preferentially. Furthermore, the purification of the desiredregioisomer (“3-oxo”) away from the undesired regioisomer can bedifficult and may require extensive column chromatography.

Reported yields for the reaction are summarised in the following table.

Reported Compound Yield Citation

21% Springer et al., 2009 (Synthesis 24) (pages 104-105)

25% Springer et al., 2009 (Synthesis 27) (pages 106-107)

15% Springer et al., 2009 (Synthesis 26) (pages 105-106)

 7%⁽¹⁾ Zambon et al., 2010 (Compound 7h) (page S8)

24% Murray et al. 2011 (Intermediate D2) (page 44) (1) Note that thereis an error in the publication; the reported yield of 240 mg correspondsto a 7% yield, not a 9% yield.

As described herein, the present inventors have determined that thesynthetic method can be very greatly improved (e.g., higher yield;preferential formation of desired regioisomer) by employing a differentreagent (i.e., glyoxylic acid), especially under certain reactionconditions, including, in particular, a large excess of glyoxylic acid(i.e., a molar excess of at least about 2).

Cyclisation Using Glyoxylic Acid

The use of glyoxylic acid in methanol for the synthesis of thepyridopyrazinone bicyclic system has been reported in a limited numberof publications. In each case, the pyridopyrazinone compoundssynthesised were either unsubstituted on the pyridyl ring, orsubstituted with halogen at the 5-position of the pyridyl ring.

Bekerman et al., 1992, describes the reaction of unsubstituted2,3-daminopyridine with glyoxylic acid and derivatives in a number ofsolvents. In methanol, the reaction constant for the undesiredregioisomer (“2-oxo”) is higher than the reaction constant for thedesired regioisomer (“3-oxo”). In chloroform, the ratio is even higherin favour of the undesired regioisomer. In aqueous media, the desiredregioisomer is formed preferentially; however, these conditions are notsuitable for water insoluble compounds.

Milbank et al., 2011, describes the synthesis of7-bromopyrido[2,3-b]pyrazin-3(4H)-one from 5-bromopyridine-2,3-diamineand glyoxylic acid in methanol. However, the isomers were obtained as amixture and were not separated.

Ballell et al., 2008, describes the same synthesis in water, where theundesired 7-bromopyrido[2,3-b]pyrazin-2(1H)-one is obtained as the majorisomer in 66% yield. Similarly, the undesired7-fluoropyrido[2,3-b]pyrazin-2(1H)-one was obtained as the major isomerin 54% yield.

To date, there has been no report of the use of a corresponding methodfor the synthesis of 4-substituted pyrido[2,3-b]pyrazin-2(1H)-ones.Therefore, the regioselectivity of the cyclisation reaction could nothave been predicted with reasonable certainty. Furthermore, the highregioselectivity demonstrated by the inventors and described herein issurprising and unexpected.

Additional publications which describe the use of glyoxylic acid or aglyoxylic acid ester for cyclisation include the following: Abosolo etal., 1990; Bates et al., 1990; Bergman et al., 1996; Clark-Lewis et al.,1957; Cushman et al., 1992; Dettner et al., 1996; Dubey et al., 2001;Leese et al., 1955; Mashelkar et al., 2006; McKillop et al., 1997; Recket al., 2011; Remli et al., 1989; Rudy et al., 1938; Seki et al., 1995;Sherman et al., 2007; Ziegler et al., 1949.

SUMMARY OF THE INVENTION

One aspect of the invention pertains to a method of preparing a compoundof Formula (3), as described herein:

Another aspect of the present invention pertains to a compound ofFormula (3) obtained by a method of synthesis as described herein, or amethod comprising a method of synthesis as described herein.

Another aspect of the invention pertains to method of chemical synthesiswhich include, as part of the chemical synthesis, a method of preparinga compound of Formula (3), as described herein.

Another aspect of the present invention pertains to novel intermediates,as described herein, which are suitable for use in the methods ofsynthesis described herein.

Another aspect of the present invention pertains to the use of suchnovel intermediates, as described herein, in the methods of synthesisdescribed herein.

As will be appreciated by one of skill in the art, features andpreferred embodiments of one aspect of the invention will also pertainto other aspects of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have determined that the synthesis of8-(4-aminophenyoxy)-4H-pyrido[2,3-b]pyrazin-3-one and related compounds(denoted herein as (3)) from 4-(4-aminophenyoxy)pyridine-2,3-diamine andrelated compounds (denoted herein as (1)) can be very greatly improved(e.g., higher yield; preferential formation of the desired regioisomer)by employing a different reagent (i.e., glyoxylic acid; denoted hereinas (2)) under certain reaction conditions, including, in particular, alarge excess of glyoxylic acid (i.e., a molar excess of at least about2).

Cyclization Step

One aspect of the present invention is a method of preparing a compoundof Formula (3):

comprising reacting a compound of Formula (1):

with a compound of Formula (2):

in a reaction mixture under cyclisation conditions to form said compoundof Formula (3);wherein the ratio of the amount of the compound of Formula (2) to theamount of the compound of Formula (1), on a molar basis, is at leastabout 2; andwherein:

-   -   —R¹ is independently —H or —R^(1A);    -   —R² is independently —H or —R^(2A);    -   —R^(1A) is independently —F, —Cl, —Br, —I, —R^(X), —OH, —OR^(X),        or —SR^(X);    -   —R^(2A) is independently —F, —Cl, —Br, —I, —R^(X), —OH, —OR^(X),        or —SR^(X);    -   each —R^(X) is independently linear or branched saturated        C₁₋₄alkyl;    -   or —R¹ and —R₂ together form —CH═CH—CH═CH—, —N═CH—CH═CH—,        —CH═N—CH═CH—, —CH═CH—N═CH—, or —CH═CH—CH═N—; and    -   —NPG is a protected amino group which is stable to said        cyclisation conditions.

Note that tautomerisation is possible on the3-oxo-3,4-dihydropyrido[3,2-b]pyrazin-8-yl group of compounds of Formula(3), as shown below. Unless otherwise indicated, a reference to onetautomer is intended to be a reference to both tautomers.

is a tautomer of

For the avoidance of doubt: n-propyl is abbreviated as -nPr; iso-propylis abbreviated as -iPr; n-butyl is abbreviated as -nBu; iso-butyl isabbreviated as -iBu; sec-butyl is abbreviated as -sBu; tert-butyl isabbreviated as -tBu; and phenyl is abbreviated as -Ph.

The Group —R¹

In one embodiment, —R¹ is —H.

In one embodiment, —R¹ is —R^(1A).

The Group —R²

In one embodiment, —R² is —H.

In one embodiment, —R² is —R^(2A).

The Group —R^(1A)

In one embodiment, —R^(1A), if present, is independently —F, —Cl, —Br,or —I;

In one embodiment, —R^(1A), if present, is —F.

In one embodiment, —R^(1A), if present, is —Cl.

In one embodiment, —R^(1A), if present, is —Br.

In one embodiment, —R^(1A), if present, is —I.

In one embodiment, —R^(1A), if present, is independently —OH or —OR^(X).

In one embodiment, —R^(1A), if present, is —OH.

In one embodiment, —R^(1A), if present, is —OR^(X).

In one embodiment, —R^(1A), if present, is —SR^(X).

The Group —R^(2A)

In one embodiment, —R^(2A), if present, is independently —F, —Cl, —Br,or —I;

In one embodiment, —R^(2A), if present, is —F.

In one embodiment, —R^(2A), if present, is —Cl.

In one embodiment, —R^(2A), if present, is —Br.

In one embodiment, —R^(2A), if present, is —I.

In one embodiment, —R^(2A), if present, is independently —OH or —OR^(X).

In one embodiment, —R^(2A), if present, is —OH.

In one embodiment, —R^(2A), if present, is —OR^(X).

In one embodiment, —R^(2A), if present, is —SR^(X).

The Group —R^(X)

In one embodiment, each —R^(X), if present, is independently -Me, -Et,-nPr, -iPr, -nBu, -iBu, -sBu, or -tBu.

In one embodiment, each —R^(X), if present, is independently -Me, -Et,-nPr, or -iPr.

In one embodiment, each —R^(X), if present, is independently -Me or -Et.

In one embodiment, each —R^(X), if present, is -Me.

The Group —R¹ and —R² Taken Together

In one embodiment, —R¹ and —R₂ together form —CH═CH—CH═CH—,—N═CH—CH═CH—, —CH═N—CH═CH—, —CH═CH—N═CH—, or —CH═CH—CH═N—.

In one embodiment, —R¹ and —R₂ together form —CH═CH—CH═CH—, for example,as in:

In one embodiment, —R¹ and —R₂ together form —N═CH—CH═CH—, —CH═N—CH═CH—,—CH═CH—N═CH—, or —CH═CH—CH═N—.

The Protected Amino Group -NPG

The protected amino group, -NPG, is a protected amino group which isstable to said cyclisation conditions.

For example, the protected amino group, -NPG, is a protected amino groupwhich is stable to mildly acidic conditions (e.g., glyoxylic acid inorganic solvent, e.g., MeOH) and unreactive for nucleophilic additiontowards a carbonyl group (e.g., the aldehyde moiety of glyoxylic acidand ethyl glyoxylate). A wide range of examples of suitable protectinggroups (including methods for their formation and subsequentdeprotection) can be found, for example, in Protective Groups in OrganicSynthesis (T. Greene and P. Wuts; 4th Edition; John Wiley and Sons,2006) and Protecting Groups (Philip J. Kocienski; Thieme, 2005).

In one embodiment, -NPG is independently a protected amino group in theform of: a carbamate; an amide; an imide; or a sulfonamide.

—NPG Example a carbamate

an amide

an imide

a sulfonamide

In one embodiment, -NPG is a protected amino group in the form of acarbamate.

In one embodiment, -NPG is independently:

-   methyl carbamate;-   ethyl carbamate;-   9-fluorenylmethyl carbamate (Fmoc-NR2);-   9-(2,7-dibromo)fluorenylmethyl carbamate;-   2-chloro-3-indenylmethyl carbamate (Climoc-NR2);-   benz[f]inden-3-ylmethyl carbamate (Bimoc-NR2);-   2,7-Di-t-Butyl[9-(10,10-dioxo-10,10,10,10-tetrahydrothioxanthyl)]methyl    carbamate-   (DBD-Tmoc-NR2);-   2-trimethylsilylethyl carbamate (Teoc-NR2)-   2,2,2-trichloroethyl carbamate;-   1,1-dimethylpropynyl carbamate;-   1,1-dimethyl-2-haloethyl carbamate;-   1,1-dimethyl-2-cyanoethyl carbamate;-   t-butyl carbamate;-   cyclobutyl carbamate;-   vinyl carbamate;-   8-quinolyl carbamate;-   N-hydroxypiperidinyl carbamate;-   4,5-diphenyl-3-oxazolin-2-one;-   benzyl carbamate (Cbz-NR2);-   p-nitrobenzyl carbamate;-   3,4-dimethoxy-6-nitrobenzyl carbamate;-   2,4-dichlorobenzyl carbamate;-   5-benzisoxazolylmethyl carbamate;-   9-anthrylmethyl carbamate;-   isonicotinyl carbamate; or-   S-benzyl carbamate.

In one embodiment, -NPG is t-butyl carbamate.

In one embodiment, -NPG is a protected amino group in the form of anamide.

In one embodiment, -NPG is independently:

-   N-formyl amide;-   N-acetyl amide;-   N-chloroacetyl amide;-   N-trichloroacetyl amide;-   N-trifluoroacetyl amide;-   N-o-nitrophenylacetyl amide;-   N-o-nitrophenoxyacetyl amide;-   N-3-phenylpropionyl amide;-   N-3-(p-hydroxyphenyl)propionyl amide;-   N-2-methyl-2-(o-phenylazophenoxy)propionyl amide;-   N-4-chlorobutyryl amide;-   N-o-nitrocinnamoyl amide;-   N-picolinoyl amide;-   N—(N′-acetylmethionyl) amide; or-   N-benzoyl amide.

In one embodiment, -NPG is a protected amino group in the form of animide.

In one embodiment, -NPG is independently:

-   N-phthalimide;-   N-tetrachlorophthalimide;-   4-nitro-N-phthalimide;-   N-2,3-diphenylmaleimide; or-   N-dithiasuccinoylimide.

In one embodiment, -NPG is a protected amino group in the form of asulfonamide.

In one embodiment, -NPG is independently:

-   p-toluenesulfonamide; or-   benzenesulfonamide.

In one embodiment, -NPG is a protected amino group which, additionally,is stable to strong basic conditions (e.g., K₂CO₃ in DMF) and reductiveconditions (e.g., H₂ on Pd/C).

An example of such a group is tert-butyl carbamate.

Combinations

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination. All combinations of the embodimentspertaining to the chemical groups represented by variables (e.g., —R¹,—R^(1A), —R², —R^(2A), —R^(X), —NPG, -A, —Ar, —Y, -A¹, -A², etc.) arespecifically embraced by the present invention and are disclosed hereinjust as if each and every combination was individually and explicitlydisclosed, to the extent that such combinations embrace compounds thatare stable compounds (i.e., compounds that can be isolated,characterised, and tested for biological activity). In addition, allsub-combinations of the chemical groups listed in the embodimentsdescribing such variables are also specifically embraced by the presentinvention and are disclosed herein just as if each and every suchsub-combination of chemical groups was individually and explicitlydisclosed herein.

Glyoxylic Acid

The compound of Formula (2) is glyoxylic acid.

Glyoxylic acid (also known as oxoacetic acid; oxoethanoic acid; andformylformic acid) has the chemical formula OCHCO₂H and a molecularweight of 74.04 g/mol. It is often handled as the monohydrate,OCHCO₂H.H₂O, which has a molecular weight of 92.05 g/mol. Both aresolids at room temperature.

Excess of Glyoxylic Acid

In one embodiment, the ratio of the amount of the compound of Formula(2) to the amount of the compound of Formula (1), on a molar basis, isat least about 2.

In one embodiment, the ratio is from about 2 to about 25.

In one embodiment, the ratio is from about 2 to about 20.

In one embodiment, the ratio is from about 2 to about 15.

In one embodiment, the ratio is from about 2 to about 10.

In one embodiment, the ratio is from about 5 to about 25.

In one embodiment, the ratio is from about 5 to about 20.

In one embodiment, the ratio is from about 5 to about 15.

In one embodiment, the ratio is from about 5 to about 10.

In one embodiment, the ratio is about 10.

Slow Rate of Addition

In one embodiment, the compound of Formula (1) and the compound ofFormula (2) are combined over an addition time of at least about 30minutes to form the reaction mixture.

For the avoidance of doubt, the term “over” in the phrase “over anaddition time” is used in this context to mean that the combining occurssubstantially continuously throughout substantially all of the durationof the addition time; the term is intended to include, for example,dropwise addition, continuous flow addition, etc.

In one embodiment, the addition time is from about 30 minutes to about24 hours.

In one embodiment, the addition time is from about 1 hour to about 24hours.

In one embodiment, the addition time is from about 2 hours to about 24hours.

In one embodiment, the addition time is from about 3 hours to about 24hours.

In one embodiment, the addition time is from about 30 minutes to about18 hours.

In one embodiment, the addition time is from about 1 hour to about 18hours.

In one embodiment, the addition time is from about 2 hours to about 18hours.

In one embodiment, the addition time is from about 3 hours to about 18hours.

In one embodiment, the addition time is from about 30 minutes to about12 hours.

In one embodiment, the addition time is from about 1 hour to about 12hours.

In one embodiment, the addition time is from about 2 hours to about 12hours.

In one embodiment, the addition time is from about 3 hours to about 12hours.

In one embodiment, the addition time is from about 30 minutes to about 6hours.

In one embodiment, the addition time is from about 1 hour to about 6hours.

In one embodiment, the addition time is from about 2 hours to about 6hours.

In one embodiment, the addition time is from about 3 hours to about 6hours.

In one embodiment, the addition time is about 30 minutes.

In one embodiment, the addition time is about 1 hour.

In one embodiment, the addition time is about 2 hours.

In one embodiment, the addition time is about 3 hours.

In one embodiment, the addition time is about 6 hours.

Further Reaction Time

In one embodiment, after the compound of Formula (1) and the compound ofFormula (2) have been combined (e.g., after the addition time), thereaction is allowed to continue for a further reaction time, forexample, at the reaction temperature, optionally with stirring (i.e., ofthe reaction mixture).

In one embodiment, the further reaction time is from about 1 hour toabout 48 hours.

In one embodiment, the further reaction time is from about 1 hour toabout 36 hours.

In one embodiment, the further reaction time is from about 1 hour toabout 24 hours.

In one embodiment, the further reaction time is from about 1 hour toabout 12 hours.

In one embodiment, the further reaction time is from about 3 hours toabout 48 hours.

In one embodiment, the further reaction time is from about 3 hours toabout 36 hours.

In one embodiment, the further reaction time is from about 3 hours toabout 24 hours.

In one embodiment, the further reaction time is from about 3 hours toabout 12 hours.

In one embodiment, the further reaction time is from about 6 hours toabout 48 hours.

In one embodiment, the further reaction time is from about 6 hours toabout 36 hours.

In one embodiment, the further reaction time is from about 6 hours toabout 24 hours.

In one embodiment, the further reaction time is from about 6 hours toabout 12 hours.

In one embodiment, the reaction mixture is stirred during the furtherreaction time.

Reaction Solvent

In one embodiment, the reaction mixture further comprises a reactionsolvent.

In one embodiment, the reaction solvent is an organic solvent.

In one embodiment, the reaction solvent is an aprotic organic solvent.

In one embodiment, the reaction solvent is, or comprises, an organicnitrile (e.g., acetonitrile).

In one embodiment, the reaction solvent is, or comprises, an organicester (e.g., ethyl acetate).

In one embodiment, the reaction solvent is, or comprises, a sulfoxide(e.g., dimethylsulfoxide (DMSO)).

In one embodiment, the reaction solvent is, or comprises, an organicamide (e.g., dimethylformamide (DMF), dimethylacetamide (DMA),N-methyl-2-pyrrolidone (NMP), or a mixture of thereof).

In one embodiment, the reaction solvent is, or comprises, an aromaticorganic solvent (e.g., toluene, xylene, or a mixture thereof).

In one embodiment, the reaction solvent is, or comprises, a linear orbranched ether (e.g., diethyl ether, tert-butyl methyl ether, or amixture of thereof).

In one embodiment, the reaction solvent is, or comprises, a cyclic ether(e.g., tetrahydrofuran (THF)).

In one embodiment, the reaction solvent is, or comprises, an alcohol.

In one embodiment, the reaction solvent is, or comprises, a C₁₋₆alkylalcohol, or a mixture of two or more C₁₋₄alkyl alcohols.

In one embodiment, the reaction solvent is, or comprises, a C₁₋₄alkylalcohol, or a mixture of two or more C₁₋₄alkyl alcohols.

In one embodiment, the reaction solvent is, or comprises, MeOH, EtOH, orTHF, or a mixture thereof.

In one embodiment, the reaction solvent is MeOH, EtOH, or THF, or amixture thereof.

In one embodiment, the reaction solvent is, or comprises, MeOH, EtOH, ora mixture of MeOH and EtOH.

In one embodiment, the reaction solvent is MeOH, EtOH, or a mixture ofMeOH and EtOH.

In one embodiment, the reaction solvent is MeOH.

In one embodiment, the reaction solvent is EtOH.

In one embodiment, the reaction solvent is THF.

Amount of Solvent

In one embodiment, the volume of reaction solvent in the reactionmixture is from about 5 to about 50 L per kg of compound of Formula (1).

More specifically, in the above embodiment, the volume of reactionsolvent, measured in litres, is from about 5 to about 50 times theweight of the compound of Formula (1), measured in kilograms.

In one embodiment, the volume of reaction solvent in the reactionmixture is from about 10 to about 30 L per kg of compound of Formula(1).

In one embodiment, the volume of reaction solvent in the reactionmixture is from about 15 to about 25 L per kg of compound of Formula(1).

In one embodiment, the volume of reaction solvent in the reactionmixture is about 20 L per kg of compound of Formula (1).

When the compound of Formula (1) is tert-butylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate, which hasan empirical formula of C₁₆H₁₉FN₄O₃ and a molecular weight of 334.34g/mol, one kilogram contains about 3 moles of compound of Formula (1).Consequently, when the volume of reaction solvent is from about 5 toabout 50 L per kg of compound of Formula (1), the concentration of thecompound of Formula (1) in the reaction mixture is from about 3 mol/5 Lto about 3 mol/50 L, or from about 0.6 to about 0.06 M. Similarly, whenthe volume of reaction solvent is about 20 L per kg of compound ofFormula (1), the concentration of the compound of Formula (1) in thereaction mixture is from about 3 mol/20 L or about 0.15 M. (In thiscontext, the concentration in the reaction mixture is the theoreticalconcentration based on the amount of compound of Formula (1) and theamount of solvent used to form the reaction mixture, rather than anyactual instantaneous concentration of the compound of Formula (1) in thereaction mixture during the reaction process.)

In one embodiment, the concentration of the compound of Formula (1) inthe reaction mixture is from about 0.01 to about 1 M.

In one embodiment, the concentration of the compound of Formula (1) inthe reaction mixture is from about 0.02 to about 0.5 M.

In one embodiment, the concentration of the compound of Formula (1) inthe reaction mixture is from about 0.05 to about 0.3 M.

In one embodiment, the concentration of the compound of Formula (1) inthe reaction mixture is from about 0.05 to about 0.2 M.

In one embodiment, the concentration of the compound of Formula (1) inthe reaction mixture is about 0.10 M.

In one embodiment, the concentration of the compound of Formula (1) inthe reaction mixture is about 0.15 M.

Methods of Combining

In one embodiment, the compound of Formula (1) is dissolved in a firstsolvent to form a starting material solution before being combined withthe compound of Formula (2) to form the reaction mixture, wherein saidfirst solvent is, or forms part of, the reaction solvent.

In one embodiment, the compound of Formula (2) is dissolved in a secondsolvent to form a glyoxylic acid reagent solution before being combinedwith the compound of Formula (1) to form the reaction mixture, whereinsaid first solvent is, or forms part of, the reaction solvent.

In one embodiment:

-   -   the compound of Formula (1) is dissolved in a first solvent to        form a starting material solution before being combined with the        compound of Formula (2) to form the reaction mixture, wherein        said first solvent forms part of the reaction solvent; and    -   the compound of Formula (2) is dissolved in a second solvent to        form a glyoxylic acid reagent solution before being combined        with the compound of Formula (1) to form the reaction mixture,        wherein said second solvent forms part of the reaction solvent.

In one embodiment, the first solvent and the second solvent, if bothpresent, are the same (e.g., both methanol).

In one embodiment, the first solvent and the second solvent, if bothpresent, are different.

In one embodiment, said starting material solution is combined with saidglyoxylic acid reagent solution by adding said starting materialsolution to said glyoxylic acid reagent solution.

In one embodiment, said starting material solution is combined with saidglyoxylic acid reagent solution by adding said glyoxylic acid reagentsolution to said starting material solution.

In one embodiment, said adding (i.e., adding said starting materialsolution to said glyoxylic acid reagent solution; adding said glyoxylicacid reagent solution to said starting material solution) is addingcontinuously (e.g., over the addition time).

In one embodiment, said adding is adding continuously is by dropwiseaddition.

In one embodiment, said adding is adding continuously is by continuousflow addition.

In one embodiment, the compound of Formula (2) is added as a solid tosaid starting material solution.

In one embodiment, the compound of Formula (2) is added as a solid tosaid starting material solution continuously (e.g., over the additiontime).

In one embodiment, the compound of Formula (1) is added as a solid tosaid glyoxylic acid reagent solution.

In one embodiment, the compound of Formula (1) is added as a solid tosaid glyoxylic acid reagent solution continuously (e.g., over theaddition time).

Reaction Temperature

In one embodiment, the temperature of the reaction mixture during thereaction is, or is maintained at, a temperature of from about 0° C. toabout the reflux temperature of the reaction mixture.

In one embodiment, the temperature of the reaction mixture during thereaction is a temperature of from about 0° C. to about the refluxtemperature of the reaction mixture.

In one embodiment, the temperature of the reaction mixture during thereaction is maintained at a temperature of from about 0° C. to about thereflux temperature of the reaction mixture.

In one embodiment, the temperature range is from about 0° C. to about78° C.

In one embodiment, the temperature range is from about 0° C. to about30° C.

In one embodiment, the temperature range is from about 0° C. to about25° C.

In one embodiment, the temperature range is from about 5° C. to about30° C.

In one embodiment, the temperature range is from about 5° C. to about25° C.

In one embodiment, the temperature range is from about 10° C. to about30° C.

In one embodiment, the temperature range is from about 10° C. to about25° C.

In one embodiment, the temperature range is from about 15° C. to about25° C.

In one embodiment, the temperature is about 20° C.

Combinations

As discussed above, certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination. All combinations of the embodimentspertaining to the reaction conditions (e.g., proportions of reagents;rate of addition of reagents; solvents; proportions of solvents; methodsfor combining reagents; temperature; etc.) are specifically embraced bythe present invention and are disclosed herein just as if each and everycombination was individually and explicitly disclosed, to the extentthat such combinations are compatible. In addition, all sub-combinationsof the reaction conditions listed in the embodiments describing suchreaction conditions are also specifically embraced by the presentinvention and are disclosed herein just as if each and every suchsub-combination of reaction conditions was individually and explicitlydisclosed herein.

Optional Subsequent Steps

In one embodiment, the method further comprises a subsequent step (a“deprotection step”) of deprotecting the protected amino group, forexample, deprotecting a compound of Formula (3):

to give a compound of Formula (4):

In one embodiment, the method further comprises a subsequent step (a“urea formation step”) of reacting the resulting amino group with asuitable 5-activated-3-tert-butyl-1-aryl-pyrazole, for example, reactinga compound of Formula (4):

with a compound of Formula (5):

to give a compound of Formula (6):

wherein:

-   -   -A is an activating group suitable for reaction with —NH₂ to        form a urea group; and    -   —Ar is phenyl, pyridyl, or naphthyl, and is optionally        substituted with one or more groups —Y, wherein each —Y is        independently selected from halo (e.g., —F, —Cl, —Br, or —I);        linear or branched saturated C₁₋₄alkyl (e.g., -Me, -Et); linear        or branched saturated C₁₋₄haloalkyl (e.g., —CF₃); —OH; linear or        branched saturated C₁₋₄alkoxy (e.g., —OMe, —OEt); and linear or        branched saturated C₁₋₄haloalkoxy (e.g., —OCF₃).

Alternatively, in one embodiment, the method further comprisessubsequent steps (an “amino activation step” followed by a “ureaformation step”) of activating the resulting amino group, followed byreaction with a 5-amino-3-tert-butyl-1-aryl-pyrazole, for example,activating a compound of Formula (4):

to give a compound of Formula (7):

and the reacting the compound of Formula (7) with a compound of Formula(8):

to give a compound of Formula (6):

wherein:

-   -   -A is an activating group suitable for reaction with —NH₂ to        form a urea group; and    -   —Ar is phenyl, pyridyl, or naphthyl, and is optionally        substituted with one or more groups —Y, wherein each —Y is        independently selected from halo (e.g., —F, —Cl, —Br, or —I);        linear or branched saturated C₁₋₄alkyl (e.g., -Me, -Et); linear        or branched saturated C₁₋₄haloalkyl (e.g., —CF₃); —OH; linear or        branched saturated C₁₋₄alkoxy (e.g., —OMe, —OEt); and linear or        branched saturated C₁₋₄haloalkoxy (e.g., —OCF₃).

In one embodiment, —Ar is phenyl or pyridyl, and is optionallysubstituted with one or more groups —Y.

In one embodiment, —Ar is phenyl, and is optionally substituted with oneor more groups —Y.

In one embodiment, —Ar is phenyl, and is optionally substituted with onegroup —Y.

In one embodiment, —Ar is phenyl, and is optionally substituted with onegroup —Y at the meta-position (e.g., as shown below).

In one embodiment, —Ar is phenyl (i.e., unsubstituted phenyl).

In one embodiment, —Y (or each —Y, if there is more than one) isindependently selected from —F, -Me, —CF₃, —OH, and —OMe.

In one embodiment, -A is a carbamate group (i.e., —NH—C(═O)OR).

In one embodiment, -A is —NH—C(═O)O-Ph.

In one embodiment, -A is —NH—C(═O)O-(4-nitrophenyl).

In one embodiment, -A is —NH—C(═O)O—C(CH₃)═CH₂.

In one embodiment, -A is —NH—C(═O)O—(N-succinimidyl) (shown below).

Suitable carbamates can be obtained, for example, by the reaction of thecorresponding amine with a suitable chloroformate (e.g., phenylchloroformate, 4-nitrophenyl chloroformate, 1-methylvinylchloroformate,etc.) or a suitable carbonate (e.g., N,N-disuccinimidyl carbonate).

In one embodiment, -A is an isocyanate group (i.e., —NCO).

Suitable isocyanates can be obtained, for example, by the conversion ofthe corresponding amine using, for example, phosgene, triphosgene, ortheir derivatives, or by conversion of the corresponding carboxylic acidto acyl azides using, for example, diphenyl phosphoryl azide, followedby a Curtius rearrangement.

Optional Preceding Steps

In one embodiment, the method further comprises a preceding step (a“nitro reduction step”) of reducing a nitro group to form an aminogroup, for example, reducing a compound of Formula (9):

to give a compound of Formula (1):

In one embodiment, the method further comprises a preceding step (a“coupling step”) of coupling a suitable 4-activated-N-protected-anilinewith a suitable 4-activated-2-amino-3-nitropyridine, for example,reacting a compound of Formula (10):

with a compound of Formula (11):

to give a compound of Formula (9):

wherein -A¹ and -A² are activating groups suitable for reaction witheach other to form an ether group, for example, in suitable reactionconditions.

In one embodiment, -A¹ is —OH.

In one embodiment, -A² is halogen (e.g., —F, —Cl, —Br, —I), cyano (i.e.,—CN), acyloxy (e.g., —OC(═O)Me), sulfonate (e.g., —OS(═O)₂Me,—OS(═O)₂CF₃, —OS(═O)₂Ph, —OS(═O)₂(4-methylphenyl), etc.), sulfonyl(e.g., —S(═O)₂Me), sulfinyl (e.g., —S(═O)Me), nitro (i.e., —NO₂), adiazonium salt (i.e., —N(+)≡N), or an ammonium salt (e.g., —N(+)Me₃).

In one embodiment, -A¹ is —OH and -A² is halogen (e.g., —F, —Cl, —Br,—I).

In one embodiment, -A¹ is —OH and -A² is —Cl.

Multi-Step Synthesis

Thus, in one embodiment, the cyclisation method described herein formspart of a multi-step synthesis, as illustrated in the following schemes,to give target compounds which are useful, for example, as anti-canceragents.

Detailed Study of Reaction Conditions

The synthetic step illustrated in the following scheme was studied indetail. SM denotes “starting material”; GA denotes “glyoxylic acid”; DRdenotes desired regioiosmer (i.e., 3-oxo regioisomer); and UR denotesundesired regioisomer (i.e., 2-oxo regioisomer).

Reagent A: 500 mg of tert-butylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate (“startingmaterial”, denoted SM) was dissolved in a solvent (denoted SM solvent),specifically, a volume (denoted SM solvent volume, SMSV) of the SMsolvent. The mixture was warmed if necessary, and then allowed to coolto room temperature.

Reagent B: An amount of glyoxylic acid (denoted GA), handled asglyoxylic acid monohydrate, was provided. Either it was used as thesolid (without solvent), or it was dissolved in the same solvent (i.e.,the SM solvent), specifically, a volume (denoted GA solvent volume,GASV) of the SM solvent, and stirred at room temperature to provide acolourless solution.

In Studies 1-8, Reagent B was added to Reagent A over an addition time(denoted AT), while the resulting reaction mixture was maintained at areaction temperature (denoted XT).

In Studies 9-34, Reagent A was added to Reagent B over an addition time(denoted AT), while the resulting reaction mixture was maintained at areaction temperature (denoted XT).

The reaction mixture was then stirred overnight, and the proportions(molar %) of starting material (SM), desired regioisomer (DR), andundesired regioisomer (UR) in the resulting product was determinedspectroscopically by HPLC (i.e., giving spectroscopic yields).

In this context, the solvent volume (i.e., the SM solvent volume and GAsolvent volume) is reported in units of “volumes”, where one “volume” isthe numerical equivalent, in litres, of the weight of the startingmaterial, SM, in kilograms. (In a sense, the solvent is treated as if ithad a density of 1 g/cm³, and 1 volume is that volume of solvent whichhas the same weight as the starting material, SM.) And so, in Study 7described below, 500 mg (i.e., 0.5 g) of SM was dissolved in 25 volumesof SM solvent (i.e., 25×0.5 mL=12.5 mL) and 2 equivalents of glyoxylicacid monohydrate was dissolved in 1 volume of SM solvent (i.e., 1×0.5mL=0.5 mL). Similarly, in Study 33 described below, 500 g (i.e., 0.5 kg)of SM was dissolved in 10 volumes of SM solvent (i.e., 10×0.5 L=5 L) and10 equivalents of glyoxylic acid monohydrate was dissolved in 10 volumesof SM solvent (i.e., 10×0.5 L=5 L).

In these studies, the SM is tert-butylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate, which hasan empirical formula of C₁₆H₁₉FN₄O₃ and a molecular weight of 334.34g/mol; consequently, one kilogram contains about 3 moles of SM. And so,in Study 7 described below, the theoretical concentration of SM in thereaction mixture is about 1.5 mmol in 13 mL, or about 0.115 M.Similarly, in Study 33 described below, the theoretical concentration ofSM in the reaction mixture is about 1.5 mol in 10 L, or about 0.15 M.

Study SM SMSV GASV GA XT SM DR UR No. solv. (vol.) (vol.) (eq.) (° C.)AT Notes % % % 1 MeOH 25 none 2 20 30 sec (a) 4 43 52 2 EtOH 25 none 220 30 sec (a) 2 34 60 3 THF 25 none 2 20 30 sec (a) 5 25 66 4 MeOH 25none 10 20 30 sec (a) 4 77 19 5 EtOH 25 none 10 20 30 sec (a) 3 55 40 6THF 25 none 10 20 30 sec (a) <0.5 83 17 7 MeOH 25 1 2 65 30 sec (a) <0.535 63 8 EtOH 25 1 2 78 30 sec (a) <0.5 25 70 9 MeOH 10 10 5 20 30 min 366 31 10 MeOH 10 10 5 0 30 min <1 71 29 11 MeOH 10 10 5 60 30 min <1 6040 12 MeOH 10 10 10 20 30 min 3 78 19 13 MeOH 10 10 10 20 30 min (b) <171 17 14 MeOH 10 10 2 65 30 min <1 35 63 15 EtOH 10 10 2 78 30 min <1 2570 16 MeOH 10 10 10 20 30 min (c) 19 66 19 17 MeOH 4 4 10 20 30 min 1170 18 18 MeOH 10 10 10 20 3 hr 3 87 10 19 MeOH 10 10 10 20 3 hr (d) <188 11 20 MeOH 8 2 10 20 3 hr 5 78 18 21 MeOH 8 2 10 20 6 hr <1 74 25 22MeOH 10 10 10 20 6 hr <1 89 10 23 MeOH 10 10 5 20 30 min 3 66 31 24 MeOH10 10 5 0 30 min <1 71 29 25 MeOH 10 10 5 60 30 min <1 60 39 26 MeOH 1010 2 20 2 hr (e) <1 26 72 27 MeOH 10 10 5 20 3 hr (f) <1 79 19 28 MeOH10 10 2 20 2 hr (g) 79 10 9 29 MeOH 10 10 10 20 3 hr (h) <1 85 13 30MeOH 15 10 10 20 3 hr (h) 1.6 83 14 31 MeOH 10 10 10 20 3 hr (i) 1 83 1432 MeOH 10 10 10 20 4.5 hr (h), (j) <1 83 15 33 MeOH 10 10 10 20 6.5 hr(h), (k) <1 89 10 34 MeOH 10 10 10 20 6.0 hr (h), (k) <1 89 10 Legendand Notes: SM = starting material. GA = glyoxylic acid. SMSV = startingmaterial solvent volume. GASV = glyoxylic acid solvent volume. DR =desired regioisomer. UR = undesired regioisomer. XT = reactiontemperature. AT = addition time. (a) Glyoxylic acid added in one portionover 30 seconds. (b) Glyoxylic acid stripped out with EtOH (2 × 10 mL)to remove water. (c) Anhydrous MgSO₄ (250 mg) added to remove water. (d)MeOH was anhydrous MeOH. (e) AcOH (10 eq.) also added. (f) AcOH (5 eq.)also added. (g) Concentrated H₂SO₄ (10 eq.) also added. (h) MeOH was“drum” MeOH. (i) Glyoxylic acid was oven-dried overnight before use. (j)Performed on a larger scale, with 50 g of SM. (k) Performed on a largerscale, with 500 g of SM.

Studies 1-8: The addition of glyoxylic acid in one portion gave anexcellent ratio at room temperature, but the ratio became worse atreflux. However, this method of addition was not suitable for use atlarger scales. The results also showed that a large excess of glyoxylicacid was required.

Studies 9-17: Performing the reaction at higher than ambient temperatureled to a worse ratio. The reaction can be performed at 0° C., but thisdoes not improve the profile. The use of MgSO₄ to remove water or usinganhydrous MeOH made no difference.

Studies 20-25: MeOH was found to give a slightly better ratio, ascompared to EtOH. Addition times of 3 to 6 hours at 20° C. using 10equivalents of glyoxylic acid monohydrate in 20 volumes (total) of MeOHgave the best profile.

Studies 26-31: The HPLC results indicate that moisture in the reactionmixture is not detrimental. This is also demonstrated by the use of drumMeOH as compared to the more expensive HPLC MeOH and oven-drying theglyoxylic acid monohydrate (which is hygroscopic) prior to use, neitherof which improved the profile. Efforts to reduce the equivalents ofglyoxylic acid monohydrate from 10 to 5 with addition of another (e.g.,cheaper) acid (AcOH or H₂SO₄) led to a worse regioisomer ratio.

Study 32: A further study on a larger scale (50 g), based on theconditions used in Study 22, gave a spectroscopic yield of 83%.Different work-ups of the product were then studied in separate runs tooptimize the isolated yield (i.e., the yield after work-up andpurification). Work-up 1: Concentration of the reaction mixture in vacuoand an EtOH recrystallisation (10 vols) gave a 48% yield. Work-up 2:Concentration of the reaction mixture in vacuo and a MeOH slurry (3vols) gave a 64% yield. Work-up 3: Cooling of the reaction mixture to 0°C. for 1 hour before filtering gave a 60% yield. Work-up 4: Removal ofapproximately half the volume of MeOH in vacuo, cooling to 0° C. for 1°hour, and filtering gave a 69% yield; the product contained 1-2% wt/wtglyoxylic acid monohydrate (starting material), which was removed via awater slurry.

Studies 33-34: Two further studies on an even larger scale (500 g),based on the conditions used in Study 22, gave a spectroscopic yield of89%. For Study 34, see also Synthesis 3 below, where an isolated yieldof 67% was obtained.

Chemical Synthesis

The syntheses described below relate to tert-butylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate. However, itis believed that same conditions can be applied to structurally similaranalogs, as described herein (i.e., with corresponding groups —R¹, —R²,and -NPG).

Synthesis 1 tert-ButylN-[4-[(2-amino-3-nitro-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate

To a 50 L flange flask was charged tert-butyl(2-fluoro-4-hydroxyphenyl)carbamate (2840 g active, 12.50 mol) anddimethylformamide (DMF) (18.5 L) followed by2-amino-3-nitro-4-chloropyridine (2083 g, 12.00 mol) and K₂CO₃ (2420 g,17.51 mol). DMF (3.5 L) was used for washings. The mixture was heated at60-65° C. for 5 hours (HPLC showed <2% starting material) before beingallowed to cool to room temperature overnight. The batch was split intotwo halves, and to each half water (16 L) was added dropwise at <30° C.(exothermic addition) and the mixture stirred for 1 hour. The solidswere filtered off, washed with water (2×5 L) and then oven dried at 60°C. to give 4100 g of the title compound as a dark solid (>95% byHPLC, >95% by NMR, 90% yield).

A total of 7127 g tert-butyl (2-fluoro-4-hydroxyphenyl)carbamate wasprocessed which provided 10431 g tert-butyl(4-((2-amino-3-nitropyridin-4-yl)oxy)-2-fluorophenyl)carbamate (91%overall yield).

Batch no. Carbamate Reagent Product Yield 1 2840 g active 4100 g active90% 2 2678 g active 3828 g active 89% 3 1609 g active 2503 g active 97%TOTAL 7127 g active 10431 g active  91%

Synthesis 2 tert-ButylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate

To a 50 L vessel was charged 5% Pd/C (128 g, 50% wet) and MeOH (23 L).tert-Butyl(4-((2-amino-3-nitropyridin-4-yl)oxy)-2-fluorophenyl)carbamate (2560 g,7.03 mol) was charged followed by a MeOH wash (2.6 L). The slurry wasstirred at 20-25° C. whilst gassing with H₂ (3 h) and then stirredovernight under an H₂ atmosphere. After this time, approximately 30% ofthe starting material remained, so additional 5% Pd/C (128 g, 50% wet)was charged, and the mixture sparged with H₂ for a further 4 hours. Thereaction mixture was stirred overnight under an H₂ atmosphere and wascomplete by HPLC. The catalyst was filtered off and MeOH (5.7 L) usedfor washings. The filtrate was concentrated in vacuo, stripped with EtOH(5 L), and oven dried to give 2355 g of the title compound in 100%yield. Purity >95% by NMR and HPLC.

A total of 10431 g tert-butyl(4-((2-amino-3-nitropyridin-4-yl)oxy)-2-fluorophenyl)carbamate wasprocessed, which provided 9478 g tert-butyl(4-((2,3-diaminopyridin-4-yl)oxy)-2-fluorophenyl)carbamate (99% overallyield).

Batch no. Nitro Reagent Product Yield 1 2560 g active 2355 g 100%  21540 g active 1392 g 98% 3 6331 g active 5731 g 99% TOTAL 10431 gactive  9478 g 99%

Synthesis 3 tert-Butyl(2-fluoro-4-((3-oxo-3,4-dihydropyrido[2,3-b]pyrazin-8-yl)oxy)phenyl)carbamate

(As described above in Study 34.) To a 20 L flask was charged glyoxylicacid monohydrate (1376 g, 14.95 mol) and MeOH (5 L). The mixture wasstirred at room temperature to provide a colourless solution. tert-ButylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate (500 g,1.495 mol) was dissolved in MeOH (5 L) via warming to 40° C. Thesolution was allowed to cool to room temperature and added dropwise tothe reaction vessel over 6.5 hours at 18-22° C. (no exotherm observed)and the reaction mixture was then stirred overnight. HPLC (220 nm)showed 89% product, 10% regioisomer, <1% starting material. The reactionmixture was stripped to approximately one-half volume on a rotavapor at40° C., before being cooled to 0° C. for 1 hour. The solids werefiltered off, washed with cold MeOH (500 mL), and then water (500 mL) toremove any residual glyoxylic acid monohydrate. The solid was driedovernight in a vacuum oven at 45° C. to provide 414 g of the titlecompound in 74% yield (purity >97% by NMR, >99% by HPLC).

The product was combined with two crude batches of product obtainedusing 50 g and 500 g tert-butylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate and adsorbedonto silica (1400 g). The material was purified by column chromatographyon silica (4 kg) eluting with 30% THF/DCM (40 L) then 40% THF/DCM (40L). The product fractions were combined and concentrated to give 906 gproduct. This was slurried in 1:1 Et₂O:heptane (8 L) for 1 hour at roomtemperature before being filtered off and washed with heptane (1 L). Thematerial was oven dried to provide 842.2 g product, which contained ˜7%solvent by NMR (5% THF, 2% DCM). Total active=783 g (67% yield).Purity >97% by NMR (excluding solvents) and >99% by HPLC.

In summary, a total of 1050 g tert-butylN-[4-[(2,3-diamino-4-pyridyl)oxy]-2-fluoro-phenyl]carbamate wasprocessed to give 783 g tert-butyl(2-fluoro-4-((3-oxo-3,4-dihydropyrido[2,3-b]pyrazin-8-yl)oxy)phenyl)carbamatein a 67% yield (following a silica plug column to remove baselineimpurities).

Synthesis 4 8-(4-amino-3-fluoro-phenoxy)-4H-pyrido[2,3-b]pyrazin-3-one

To a 10 L flask was charged tert-butyl(2-fluoro-4-((3-oxo-3,4-dihydropyrido[2,3-b]pyrazin-8-yl)oxy)phenyl)carbamate(783 g, 2.10 mol) and 1 M tetra-n-butylammonium fluoride (TBAF) intetrahydrofuran (THF) (8.5 L, 8.5 mol). The mixture was heated to refluxand the temperature maintained for 30 hours. HPLC indicated the reactionwas complete. The THF was removed in vacuo and MeOH (8 L) added to thecrude black oil. The resulting slurry was stirred for 1 hour, filtered,and washed with MeOH (1 L). ¹H NMR analysis showed approximately 11%TBAF was present; therefore, the material was re-slurried in MeOH (8 L)for 1 hour, filtered, and washed with MeOH (1 L). The product was driedat 45° C. overnight to afford 415 g of the title compound (NMR >95%,HPLC >97%, <1% TBAF by NMR, 72% yield).

A total of 2217 g tert-butyl(2-fluoro-4-((3-oxo-3,4-dihydropyrido[2,3-b]pyrazin-8-yl)oxy)phenyl)carbamatewas deprotected using the TBAF method to provide 1208.5 g8-(4-amino-3-fluorophenoxy)pyrido[2,3-b]pyrazin-3(4H)-one in 75% yield.

Batch no. Protected Reagent Product Yield 1 783 g active 415 g 72% 2 735g active 379.5 g 71% 3 699 g active 414 g 81% TOTAL 2217 g active 1208.5 g 75%

Synthesis 5 5-tert-Butyl-2-(3-fluorophenyl)pyrazol-3-amine

A mixture of 4,4-dimethyl-3-oxopentane nitrile (77 g, 0.62 mol) and3-fluorophenylhydrazine hydrochloride (100 g, 0.62 mol) was added totoluene (1 L) and heated to 100° C. (reflux) for 24 hours. The reactionmixture was then allowed to cool to 20° C. The reaction mixture was thenfiltered, washed with toluene (2×250 mL), and dried in vacuo. The crudeHCl salt was combined with a previous batch (performed using 180 g of3-fluorophenylhydrazine hydrochloride) and partitioned between DCM (4 L)and sat. aq. NaHCO₃ (4 L). The mixture was stirred until no solidremained. The DCM layer was separated off, dried (MgSO₄), filtered, andconcentrated in vacuo to provide the title compound as an orange solid(210 g) in 52% yield. Purity >95% by NMR and 94.4% by LCMS.

Synthesis 6 PhenylN-[5-tert-butyl-2-(3-fluorophenyl)pyrazol-3-yl]carbamate

5-tert-Butyl-2-(3-fluorophenyl)pyrazol-3-amine (210 g, 0.90 mol) wasdissolved in THF (5 L) at 0° C. before the addition of pyridine (146 mL,1.80 mol). Phenyl chloroformate (113 mL, 0.90 mol) in THF (300 mL) wascharged dropwise at 0-5° C. over 30 minutes. The reaction mixture wasstirred at 0° C. for 30 minutes, and then allowed to warm to roomtemperature. After 4 hours, HPLC showed 8% stage 1 remained. A furthercharge of phenyl chloroformate (11 mL, 0.088 mol) was added, and after30 minutes, HPLC analysis indicated the reaction was complete. EtOAc (5L) was charged and the organic layer washed with 1 M HCl (2×1.2 L),water (1.2 L), sat. aq. NaHCO₃ (1.2 L) and sat. brine (1.2 L). Theorganic layer was dried (MgSO₄), filtered, and concentrated in vacuo.The crude oil was taken up in a 1:3 mixture of EtOAc:heptane andconcentrated in vacuo to give a solid. The solid was slurried in heptane(2.5 L) for 1 hour, filtered, and washed with heptane (200 mL). Thematerial was oven dried at 40° C. overnight to afford the title compound(286 g) in 90% yield. Purity >95% by NMR.

Synthesis 71-[2-Fluoro-4-[(3-oxo-4H-pyrido[2,3-b]pyrazin-8-yl)oxy]phenyl]-3-[2-(3-fluorophenyl)pyrazol-3-yl]urea

To 8-(4-amino-3-fluorophenoxy)pyrido[2,3-b]pyrazin-3(4H)-one (169.5 g,0.623 mol) was charged phenylN-[3-tert-butyl-1-(3-fluorophenyl)-1H-pyrazol-5-yl]carbamate (220 g,0.623 mol) and DMSO (1.7 L). The reaction mixture was stirred at 20-22°C. overnight. ¹H NMR indicated that the reaction was complete. Thereaction mixture was quenched into water (8.6 L) and stirred for 1 hourbefore being filtered and washed with water (2×2 L). The material wasoven dried at 60° C. over the weekend. The solid was slurried in EtOAc(3.39 L) for 1 hour, filtered, and washed with EtOAc (750 mL) to give320 g of product. NMR indicated phenol was still present. The materialwas re-slurried in EtOAc (3.2 L) for 1 hour, filtered, and washed withEtOAc (500 mL) and dried to afford 293 g of the title compound (9% EtOAcby NMR, one single impurity 0.8%). The solid was recrystallised from THF(5.7 L) and heptane (2.85 L) as follows: THF was added and the mixtureheated to reflux to achieve a solution. Heptane was then added over 40minutes at 66° C. and the solution seeded at 60° C.; the batch was thenallowed to cool to room temperature before filtering off the solids. Thefilter cake was washed with heptane (2.85 L) and oven dried at 45° C.overnight to give 211 g of title compound (64% yield).

Synthesis 8 tert-ButylN-[4-[(3-oxo-4H-pyrido[2,3-b]pyrazin-8-yl)oxy)-1-naphthyl)carbamate

Glyoxylic acid monohydrate (2.75 g, 30 mmol) was dissolved in MeOH (10mL). A solution of tert-butyl(4-((2,3-diaminopyridin-4-yl)oxy)naphthalen-1-yl)carbamate (1.1 g, 3mmol) (for synthesis, see, e.g., Menard et al., 2009) in 25 mL MeOH wasprepared by heating the flask until no more solid remained. Thissolution was added dropwise (slowly over 3 hours) to the stirredsolution of glyoxylic acid. After stirring overnight, a precipitate wasformed. The reaction mixture was concentrated and the solid recovered byfiltration and washed with 10 mL cold MeOH, and then with water. Thecake was dried to afford the desired regioisomer (according to NMR, ascompared to reported literature compound), yield 627 mg (50%).

Comparison with Known Methods

As summarised below, the methods described herein provide asubstantially improved yield, as compared to the known method, forexample, an increase from 25% to 67-74% and an increase from 7% to 50%.

Comparison 1 Desired Regioisomer Undesired Regioisomer

Known Spect. Not determined Not determined method⁽¹⁾ Yield Isolated 25%69% Yield Present Spect. 89% 10% method⁽²⁾ Yield Isolated 74%/67% Notisolated Yield (1): Zambon et al., 2010: To a solution of tert-butyl4-(2,3-diaminopyridin-4-yloxy)-2-fluorophenylcarbamate (3.50 g, 10.5mmol) in dry EtOH were added consecutively molecular sieves (3Å) andethyl glyoxylate (3.6 mL of a 50% solution in toluene, 1.7 equivalents).The solution was stirred at room temperature for 3 hours until thestarting material was consumed (monitored by TLC). The desiredregioisomer was isolated to give 0.96 g product (25% yield). (2): SeeSynthesis 3 above.

Comparison 2 Desired Regioisomer Undesired Regioisomer

Known Spect. Not determined Not determined method⁽³⁾ Yield Isolated  7%42% Yield Present Spect. Not determined Not determined method⁽⁴⁾ YieldIsolated 50% Not isolated Yield (3): Zambon et al., 2010: To a solutionof tert-butyl 4-(2,3-diaminopyridin-4-yloxy)naphthalen-1-ylcarbamate(3.1 g, 8.2 mmol) in dry EtOH were added consecutively molecular sieves(3Å) and ethyl glyoxylate (2.8 mL of a 50% solution in toluene, 1.7equivalents). The solution was stirred at room temperature for 3 hoursuntil the starting material was consumed (monitored by TLC). The desiredregioisomer was isolated by chromatography with 50% ethyl acetate, togive 0.24 g product (7% yield). (Note that there is an error in thepublication; the reported yield of 240 mg corresponds to a 7% yield, nota 9% yield.) (4): See Synthesis 8 above.

REFERENCES

A number of publications are cited herein in order to more fullydescribe and disclose the invention and the state of the art to whichthe invention pertains. Full citations for these references are providedbelow. Each of these references is incorporated herein by reference inits entirety into the present disclosure, to the same extent as if eachindividual reference was specifically and individually indicated to beincorporated by reference.

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The invention claimed is:
 1. A method of preparing a compound of Formula(3):

comprising the step of reacting a compound of Formula (1):

with a compound of Formula (2):

in a reaction mixture under cyclisation conditions to form said compoundof Formula (3); wherein the ratio of the amount of the compound ofFormula (2) to the amount of the compound of Formula (1), on a molarbasis, is at least about 2; and wherein: —R¹ is independently —H or—R^(1A); —R² is independently —H or —R^(2A); —R^(1A) is independently—F, —Cl, —Br, —I, —R^(X), —OH, —OR^(X), or —SR^(X); —R^(2A) isindependently —F, —Cl, —Br, —I, —R^(X), —OH, —OR^(X), —SR^(X); each—R^(X) is independently linear or branched saturated C₁₋₄alkyl; or —R¹and —R₂ together form —CH═CH—CH═CH—, —N═CH—CH═CH—, —CH═N—CH═CH—,—CH═CH—N═CH—, or —CH═CH—CH═N—; and —NPG is a protected amino group whichis stable to said cyclisation conditions.
 2. The method according toclaim 1, wherein —R¹is —H.
 3. The method according to claim 1, wherein—R¹is —R^(1A).
 4. The method according to claim 1, wherein —R² is —H. 5.The method according to claim 1, wherein —R² is —R^(2A).
 6. The methodaccording to claim 1, wherein —R^(1A), if present, is independently —F,—Cl, —Br, or —I.
 7. The method according to claim 1, wherein —R^(1A), ifpresent, is —F.
 8. The method according to claim 1, wherein —R^(1A), ifpresent, is —OH.
 9. The method according to claim 1, wherein —R^(1A), ifpresent, is —OR^(X).
 10. The method according to claim 1, wherein—R^(1A), if present, is —SR^(X).
 11. The method according to claim 1,wherein —R^(2A), if present, is independently —F, —Cl, —Br, or —I. 12.The method according to claim 1, wherein —R^(2A), if present, is —F. 13.The method according to claim 1, wherein —R^(2A), if present, is —OH.14. The method according to claim 1, wherein —R^(2A), if present, is—OR^(X).
 15. The method according to claim 1, wherein —R^(2A), ifpresent, is —SR^(X).
 16. The method according to claim 1, wherein each—R^(X), if present, is —Me.
 17. The method according to claim 1, wherein—R¹ and —R₂ together form —CH═CH—CH═CH—, —N═CH—CH═CH —, —CH═N—CH═CH—, or—CH═CH—CH═N—.
 18. The method according to claim 1, wherein —R¹and —R₂together form —CH═CH—CH═CH—.
 19. The method according to claim 1,wherein —NPG is independently a protected amino group in the form of: acarbamate; an amide; an imide; or a sulfonamide.
 20. The methodaccording to claim 1, wherein —NPG is a protected amino group in theform of a carbamate.
 21. The method according to claim 1, wherein —NPGis tert-butyl carbamate.
 22. The method according to claim 1, wherein—NPG is a protected amino group in the form of an amide.
 23. The methodaccording to claim 1, wherein —NPG is a protected amino group in theform of an imide.
 24. The method according to claim 1, wherein —NPG is aprotected amino group in the form of a sulfonamide.
 25. The methodaccording to claim 1, wherein the ratio of the amount of the compound ofFormula (2) to the amount of the compound of Formula (1), on a molarbasis, is from about 2 to about
 25. 26. The method according to claim25, wherein said ratio is from about 2 to about
 20. 27. The methodaccording to claim 25, wherein said ratio is from about 2 to about 10.28. The method according to claim 25, wherein said ratio is from about 5to about
 15. 29. The method according to claim 25, wherein said ratio isfrom about 5 to about
 10. 30. The method according to claim wherein saidratio is about
 10. 31. The method according to claim 1, wherein thecompound of Formula (1) and the compound of Formula (2) are combinedover an addition time of at least about 30 minutes to form the reactionmixture.
 32. The method according to claim 31, wherein the addition timeis from about 30 minutes to about 24 hours.
 33. The method according toclaim 31, wherein the addition time is from about 1 hour to about 18hours.
 34. The method according to claim 31, wherein the addition timeis from about 2 hours to about 12 hours.
 35. The method according toclaim 31, wherein the addition time is from about 3 hours to about 6hours.
 36. The method according to claim 1, wherein, after the compoundof Formula (1) and the compound of Formula (2) have been combined, thereaction is allowed to continue for a further reaction time.
 37. Themethod according to claim 36, wherein the further reaction time is fromabout 1 hour to about 48 hours.
 38. The method according to claim 36,wherein the further reaction time is from about 3 hours to about 24hours.
 39. The method according to claim 36, wherein, the reactionmixture is stirred during the further reaction time.
 40. The methodaccording to claim 1, wherein the reaction mixture further comprises areaction solvent.
 41. The method according to claim 40, wherein thereaction solvent is, or comprises, an organic solvent.
 42. The methodaccording to claim 40, wherein the reaction solvent is, or comprises, analcohol, a linear or branched ether, a cyclic ether, or a mixturethereof.
 43. The method according to claim 40, wherein the reactionsolvent is, or comprises, an alcohol.
 44. The method according to claim40, wherein the reaction solvent is, or comprises, a C₁₋₄alkyl alcohol,or a mixture of two or more C₁₋₄alkyl alcohols.
 45. The method accordingto claim 40, wherein the reaction solvent is MeOH, EtOH, or THF, or amixture thereof.
 46. The method according to claim 40, wherein thereaction solvent is MeOH, EtOH, or a mixture of MeOH and EtOH.
 47. Themethod according to claim 40, wherein the reaction solvent is MeOH. 48.The method according to claim 40, Therein the volume of reaction solventin the reaction mixture is from about 5 to about 50 L per kg of compoundof Formula (1).
 49. The method according to claim 48, wherein the volumeof reaction solvent in the reaction mixture is from about 10 to about 30L per kg of compound of Formula (1).
 50. The method according to claim48, Wherein the volume of reaction solvent in the reaction mixture isfrom about 15 to about 25 L per kg of compound of Formula (1).
 51. Themethod according to claim 48, Wherein the volume of reaction solvent inthe reaction mixture is about 20 L per kg of compound of Formula (1).52. The method according to claim 40, wherein the concentration of thecompound of Formula (1) in the reaction mixture, based on the amount ofcompound of Formula (1) and the amount of solvent used to form thereaction mixture, is from about 0.01 to about 1 M.
 53. The methodaccording to claim 52, wherein. said concentration is from about 0.02 toabout 0.5 M.
 54. The method according to claim 52, wherein saidconcentration is from about 0.05 to about 0.3 M.
 55. The methodaccording to claim 52, wherein said concentration is from about 0.05 toabout 0.2 M.
 56. The method according to claim 52, wherein saidconcentration is about 0.10 M.
 57. The method according to claim 52,wherein said concentration is about 0.15 M.
 58. The method according toclaim 40, wherein the compound of Formula (1) is dissolved in a firstsolvent to form a starting material solution before being combined withthe compound of Formula (2) to form the reaction mixture, wherein saidfirst solvent is, or forms part of; the reaction solvent.
 59. The methodaccording to claim 40, wherein the compound of Formula (2) is dissolvedin a second solvent to form a glyoxylic acid reagent solution beforebeing combined with the compound of Formula (1) to form the reactionmixture, wherein said first solvent is, or forms part of, the reactionsolvent.
 60. The method according to claim 40, wherein: the compound ofFormula (1) is dissolved in a first solvent to form a starting materialsolution before being combined with the compound of Formula (2) to formthe reaction mixture, wherein said first solvent forms part of thereaction solvent; and the compound of Formula (2) is dissolved in asecond solvent to form a glyoxylic acid reagent solution before beingcombined with the compound of Formula (1) to form the reaction mixture,wherein said second solvent forms part of the reaction solvent.
 61. Themethod according to claim 60, wherein the first solvent and the secondsolvent are the same.
 62. The method according to claim 60, wherein thefirst solvent and the second solvent are different.
 63. The methodaccording to claim 60, wherein said starting material solution iscombined with said glyoxylic acid reagent solution by adding saidstarting material solution to said glyoxylic acid reagent solution. 64.The method according to claim 60, wherein said starting materialsolution is combined with said glyoxylic acid reagent solution by addingsaid glyoxylic acid reagent solution to said starting material solution.65. The method according to claim 63, wherein said adding is addingcontinuously (e.g., over the addition time).
 66. The method according toclaim 65, wherein said adding continuously is adding by dropwiseaddition.
 67. The method according to claim 65, wherein said addingcontinuously is adding by continuous flow addition.
 68. The methodaccording to claim 58, wherein the compound of Formula (2) is added as asolid to said starting material solution.
 69. The method according toclaim 58, wherein the compound of Formula (2) is added as a solid tosaid starting material solution continuously (e.g., over the additiontime).
 70. The method according to claim 59, wherein the compound ofFormula (1) is added as a solid to said glyoxylic acid reagent solution.71. The method according to claim 59, wherein the compound of Formula(1) is added as a solid to said glyoxylic acid reagent solutioncontinuously (e.g., over the addition time).
 72. The method according toclaim 1, wherein the temperature of the reaction mixture during thereaction is, or is maintained at, a temperature of from about 0° C. toabout the reflux temperature of the reaction mixture.
 73. The methodaccording to claim 72, wherein the temperature range is from about 0° C.to about 30° C.
 74. The method according to claim 72, wherein thetemperature range is from about 10° C. to about 30° C.
 75. The methodaccording to claim 72, wherein the temperature range is from about 15°C. to about 25° C.
 76. The method according to claim 72, wherein thetemperature is about 20° C.
 77. The Method according to claim 1, furthercomprising a subsequent step of deprotecting said compound of Formula(3):

to give a compound of Formula (4):


78. The method according to claim 77, further comprising a subsequentstep of reacting said compound of Formula (4):

with a compound of Formula (5):

to give a compound of Formula (6):

wherein: -A is an activating group suitable for reaction with —NH ₂ toform a urea group; and —Ar is phenyl, pyridyl, or naphthyl, and isoptionally substituted with one or more groups —Y, wherein each —Y isindependently selected from halo; linear or branched saturatedC₁₋₄alkyl; linear or branched saturated C₁₋₄haloalkyl; —OH; linear orbranched saturated C₁₋₄alkoxy; and linear or branched saturatedC₁₋₄haloalkoxy.
 79. The method according to claim 77, further comprisinga subsequent step of activating said compound of Formula (4):

to give a compound of Formula (7):

and the reacting the compound of Formula (7) with a compound of Formula(8):

to give a compound of Formula (6):

wherein: -A is an activating group suitable for reaction with —NH₂ toform a urea group; and —Ar is phenyl, pyridyl, or naphthyl, and isoptionally substituted with one or more goups —Y, wherein each —Y isindependently selected from halo; linear or branched saturatedC₁₋₄alkyl; linear or branched saturated C₁₋₄ haloalkyl; —OH; linear orbranched saturated C₁₋₄alkoxy; and linear or branched saturatedC₁₋₄haloalkoxy.
 80. The method according to claim 1, further comprisinga preceding step of reducing a compound of Formula (7):

to give said compound of Formula (1):


81. The method according to claim 80, further comprising preceding stepof reacting a compound of Formula (8):

with a compound of Formula (9):

to give said compound of Formula (7):

wherein -A^(l) and -A² are activating groups suitable for reaction witheach other to form an ether group.
 82. The method according to claim 78,wherein each —Y is independently selected from the group consisting of—F, —Cl, —Br, —I, —Me, —Et, —CF₃, —OMe, —OEt, and —OCF₃.
 83. The methodaccording to claim 79, wherein each —Y is independently selected fromthe group consisting of —F, —Cl, —Me, —Et, —CF₃—OMe, —OEt, and —OCF₃.